I don't have a 9800 pro, but try this out.
Run a benchmark with halflife2, doom3 or any other game you play regularly - run it with the lowest possible resolution (640x480?) and no AA/AF.
The score you get is basically what your cpu is capable of. So if you get 130fps in halflife2, if your computer is not video limited, you should also get 130fps in halflife2 at 1600x1200 with AA/AF turned on.
I haven't played battlefield2 yet, but lets say for example you only get 20fps in BF2 at low resolutions, and the game just seems to go slow no matter how low you turn the quality settings - then you really need to look at getting a cpu upgrade.
Overall, if you want to play high resolutions, but only low resolutions are playable, you need a new video card.
For a pure gaming system, a fast cpu is not necessary and an upgrade with a faster video card will do a lot better than a cpu/motherboard upgrade.
After looking at your sig, it looks like we've got about the same system

I have an 8rda and an XP @ 2.2ghz, but with a geforce4 video card. I ordered a geforce 6800 and will have it delivered in about 5 hours from now. I'll let you know what sort of improvement I get if you're interested.